Ilya V. Romanchenko

Repetitive sub-gigawatt rf source based on gyromagnetic nonlinear transmission line

We demonstrate a high power repetitive rf source using gyromagnetic nonlinear transmission line to produce rf oscillations. Saturated NiZn ferrites act as active nonlinear medium first sharpening the pumping high voltage nanosecond pulse and then radiating at central frequency of about 1 GHz: shock rise time excites gyromagnetic precession in ferrites forming damping rf oscillations. The optimal length of nonlinear transmission line was found to be of about 1 m. SINUS-200 high voltage driver with Tesla transformer incorporated into pulse forming line has been designed and fabricated to produce bursts of 1000 pulses with 200 Hz repetition rate. A band-pass filter and mode-converter have been designed to extract rf pulse from low-frequency component and to form TE(11) mode of circular waveguide with linear polarization. A wide-band horn antenna has been fabricated to form Gaussian distribution of radiation pattern. The peak value of electric field strength of a radiated pulse at the distance of 3.5 m away from antenna is measured to be 160 kV/m. The corresponding rf peak power of 260 MW was achieved.

Phase Control in Parallel Channels of Shock-Excited Microwave Nanosecond Oscillators

The theoretical premises and experimental results of phase control in high-power microwave oscillators with nanosecond pulse duration are presented. In experiments, two-channel backward wave oscillators (BWOs) for both steady state (100-150 cycles) and super-radiance (SR) mode operation (10-20 cycles) are discussed. For the phase control, the shift of the moment with fastest current rise is provided in the sections of nonlinear transmission lines with axially biased ferrites. The voltage pulse sharpening and shift of group velocity depend on the dc axial magnetic field. In SR mode, two-channel source is capable of producing 2 × 0.3 GW pulses with duration of 2 ns and the center frequency of 10 GHz. The source operates at the repetition rate up to 100 pps with electronic control of the phase in one channel relative to another. The last experiment is carried out using two synchronized compact RADAN-type drivers with two parallel Ka-band BWOs (100 MW, 2 ns, 37 GHz). The controllable shift of interference picture is a proof of the coherency in the aggregated radiation. At the maximum of the pattern in the far zone, the detector indicateds fourfold increase in power density over that measured from single channel.

Generation of Subgigawatt RF Pulses in Nonlinear Transmission Lines

This paper presents the experimental results on the generation of subgigawatt radio frequency (RF) pulses using two types of nonlinear transmission lines (NLTLs). In the high-voltage coaxial lines, we used the following: 1) a periodic gas gap structure and 2) uniformly loaded saturated ferrite with axial bias. The concept of the first line is based on the in-phase composition of RF fields produced by currents in the periodic gas gap structure of the inner conductor. The most stable and efficient narrow-band operation of the system with 12 cylindrical gas gaps (200 kV, 18 ns) was realized at an RF of 1 GHz and an RF power of several hundreds of megawatts. The maximum power conversion reached 10%. The second NLTL lacks spatial dispersion. The self-consistent dynamics of the traveling wave is observed by coherent magnetic switching in ferrites with axial bias. The pulsed voltage driver produced 9-ns pulses of voltage between 110 and 290 kV. With the optimum external magnetic field, the efficiency of energy conversion was 10%. The peak power of oscillations produced on a resistive load was 700 MW. An increase in central frequency from 600 MHz to 1.1 GHz with incident pulse amplitude was found.

High power microwave beam steering based on gyromagnetic nonlinear transmission lines

We demonstrate electronically controlled beam steering by high power RF pulses produced by two gyromagnetic nonlinear transmission lines (NLTLs) connected to a one high voltage driver. Each NLTL is capable of producing several ns RF pulses with peak power from 50 to 700 MW (6% standard deviation) at frequencies from 0.5 to 1.7 GHz (1% standard deviation) with 100 Hz repetition rate. Using a helix antenna allows irradiating of RF pulses with almost circular polarization and 350 MW maximum peak power, which corresponds to 350 kV effective potential of radiation. At the installation of two identical channels, we demonstrate the possibility of beam steering within ±15° in the horizontal plane by coherent RF pulses with circular polarization at 1.0 GHz center frequency. Fourfold increase in the power flux density for in-phase irradiation of RF pulses is confirmed by comparison with one-channel operation.

Formation of subnanosecond rise times of high-voltage pulses in an unsaturated-ferrite-loaded coaxial line

A high-voltage forming device in which a section of a ferrite-filled coaxial transmission line is used to sharpen the rise time of nanosecond pulses has been studied. It is shown that low-conductivity nickel-zinc ferrites are suitable for sharpening the rise time of submegavolt pulses. Experiments for two versions of the ferrite line and different lengths of the ferrite-filled sections have been performed. The experimental results indicate the possibility of sharpening the rise time of output pulses to 0.7 ns in the range of pulse amplitudes 110–360 kV at a pulse repetition rate of up to 100 Hz.

Coherent Summation of Emission From Relativistic Cherenkov Sources as a Way of Production of Extremely High-Intensity Microwave Pulses

For relativistic Cherenkov devices, we investigate the process of high-power microwave pulse generation with its phase correlating to the sharp edge of an e-beam current pulse. Our theoretical consideration is referred to quasi-stationary and superradiative (SR) generation regimes when spontaneous emission of the e-beam edge serves as the seed for the development of further coherent oscillations. Phase correlation of the excited microwave pulses with the characteristics of the current pulse front and/or an initial external electromagnetic pulse has been additionally confirmed by particle-in-cell simulations. Pulse-to-pulse stability of the radiation phase within several percents of the oscillation period makes it possible to arrange multichannel schemes producing mutually coherent microwave pulses. In the experiments that have been carried out, the cathodes of independent generators were powered by identical accelerating pulses from strictly synchronized voltage modulators, or by splitting the pulse from a single powerful modulator. For the 2-ns regime with the power of each Ka-band backward-wave oscillator about 100 MW, we demonstrate quadratic growth of the power density in the interference maximum of the directional diagram. In a short pulse SR regime, with the peak power of 600 MW in a single channel, for a four-channel 2-D array, we attained a 16-fold radiation intensity gain.

High repetition rate multi-channel source of high-power rf-modulated pulses.

This paper presents the results of testing a high voltage pulse generator based on parallel gyromagnetic nonlinear transmission lines filled with saturable ferrite. The generator is capable of producing almost identical stable rf-modulated nanosecond high voltage pulses in each of the two, or four, parallel output channels. The output voltage amplitude in each channel can reach -285 or -180 kV, respectively, with a rf modulation depth of up to 60%. Drive pulses were produced as the packets of duration 1-5 s at a pulse repetition frequency of 800 Hz using a driver equipped with all-solid-state switches. Splitting the driver pulse provided electric field strengths in the channels which were below the breakdown field strength of the transmission lines. As a result, the use of nonlinear transmission lines of reduced diameter made it possible to increase the center frequency of the excited rf oscillations to ∼2 GHz.

Effective irradiation of high-power RF pulses from gyromagnetic nonlinear transmission lines

Summary form only given. Development of HPM sources based on gyromagnetic nonlinear transmission lines (NLTLs) includes the appropriate filtration of the high voltage video pulse and the irradiation antenna. We present experimental results of testing of band-pass filters designed for NLTLs. The influence of a band-pass filter bandwidth on the irradiated RF peak power is discussed. Two antenna systems have been developed to irradiate RF pulses with peak power up to 1.4 G W. To increase the directivity of the irradiation the 4 channel splitter into four 50 Ohm loads (antenna array) has been designed and tested. The coherent parallel excitation of several NLTLs is discovered to be possible due to the low jitter - about 5% of the period of oscillations. The possibility of the elongation of the RF pulses produced in the gyromagnetic NLTLs using coupled coaxial lines with spatial dispersion is discussed.

Gyromagnetic RF source for interdisciplinary research

We demonstrate a source of high power nanosecond RF pulses based on gyromagnetic nonlinear transmission line. The source is designed to explore the exposure of different biological objects to strong RF fields in an air filled rectangular waveguide loaded onto ethanol RF load. The RF pulse amplitude can be varied by 52 dB, reaching a maximum value of nearly 40 kV/cm and decreasing to tens of V/cm. The RF pulse amplitude is controlled by decreasing the incident pulse amplitude from the high voltage driver. The duration of RF pulses lies in the range from 4 to 25 ns and the frequency from 0.6 to 1.0 GHz.

Four channel high power rf source with beam steering based on gyromagnetic nonlinear transmission lines

The synchronized operation of four gyromagnetic nonlinear transmission lines (NLTLs) was tested with a pulse repetition frequency up to 1 kHz during 1 s bursts. High voltage pulses with a duration of ∼5 ns from the solid state driver S-500 were split into four 48 Ω channels reaching about -200 kV in each channel with ∼10% variation in the amplitude. The maximum peak voltage at the NLTL output was within 220-235 kV with the maximum modulation depth of decaying oscillations up to 90% at the center frequency near 2.1 GHz. The relative delay between channels reached the half-period of the center frequency of oscillations. The associated beam steering by four element array of conical helical antennas was demonstrated in a horizontal plane at 17°. The effective potential of radiation reached 360 kV at the radiation axis. The effect of ferrite temperature on the shock wave velocity in gyromagnetic NLTL is observed.